The invention relates to a method for initiating the remote feed of electrical users by means of dc series feed, particularly intermediate stations of devices of communication transmission technology. A feed device containing a dc source is provided in a feed location and a resistance of the remote feed circuit is first checked. The remote feed current is only switched on as soon as a value of the resistance of the remote feed circuit lying below a prescribed amount is determined in the feed location.
It is known, for example, from German Letters Patent AS No. 1,902,090, which corresponds to British Letters Patent No. 1,286,033, incorporated herein by reference, to employ devices in the remote feed of electrical users for automatically closing the remote feed circuit in front of an interruption location, and particularly to employ so-called switch auxiliaries. Such devices close the remote feed circuit via a cross arm as long as no current of a prescribed size is measured in the continuing portion of the remote feed circuit. One section after another of the remote feed path is checked and, under certain conditions, hooked up in this manner when the remote feed is initiated. Thus, one can avoid placing the remote feed in operation when a resistance reaching or even exceeding a prescribed value of resistance corresponding to human body resistance is adjacent to an interrupt location.
Another embodiment of a device for closing a remote feed circuit in front of an interrupt location proceeds from the German Letters Patent AS No. 1,154,525, incorporated herein by reference.
On the other hand, a device for the remote feed of electrical users by means of dc series feed can be constructed without such switch auxiliaries, for example, in view of limited installation space. When initiating such remote feed paths, the remote feed device in the feeding location must hook up the remote feed current to the loop resistance of the complete path. However, for reasons of personal protection, completion of a hookup must be avoided when the remote feed circuit is closed at an interrupt location by means of contact via human body resistance.
As long as the remote feed current is so low that it does not exceed a value allowable upon contact, for example 40 mA, the hookup can be undertaken without additional techniques.
Given high remote feed currents, however, a check is preferably carried out before initiation to determine whether the feed loop circuit is completely closed and is not perhaps bridged by contact at an interrupt location. The difficulty accordingly arises that the loop resistance of a complete remote feed path exhibits far higher values, particularly at low test voltages or currents, than human body resistance which, for example, can be assumed at 2000 .OMEGA.. Thus, difficulties can arise since an intact loop when checking the overall remote feed loop cannot be distinguished with sufficient reliability from a remote feed loop where an interrupt location is bridged by human body resistance. It can be particularly disadvantageous that the range of the remote feed and the specific resistance of the remote feed current paths are limited in consideration of the desired check.